1. Field of the Invention
This invention relates to an improved load lifting swab cup, the reinforcement cage which is used in the manufacture of the improved swab cup and a method for the manufacture of the improved swab cup. Swab cups are categorized as well servicing equipment and can be used for tubing, casing and drill pipe.
2. Description of the Related Art
The primary purpose of a swab cup (sometimes referred to herein as a "cup") is to lift from a well a volume of fluid, such as oil, gas or water, or any other well fluid or debris. Swabbing is described as the operation of a lifting device, i.e. assembly which includes one or more swab cups, to bring well fluids to the surface when the well does not flow naturally. This is a temporary operation to determine whether or not the well can be made to flow. In the event the well does not flow after being swabbed, it is necessary to install artificial lifting devices to bring oil to the surface.
Swabbing and swab cups are used to accomplish a variety of essential functions in the drilling of wells. Typically, swabbing is described as a method of getting the well into production, but it may also be necessary to swab a well many times during its life to keep the tubing clear and to restore production after the well has been worked over. A swabbing operation is often used to clean out the foreign matter in the tubing to assist the well in coming into production. The use of swab cups is well-known in the art.
It has been the usual practice during the manufacture of swab cups of the type with which the present invention is concerned to first assemble a reinforcement cage including a base and reinforcing wires, sometimes using a jig to hold the wires in axially disposed orientation. The assembled reinforcement cage and an uncured elastomeric blank are then placed within a mold which displaces the elastomer around the wires and shapes the cup, some part of the mold frequently holding the wires circumferentially in place during the molding operation. In accordance with the teaching of the prior art, and depending upon the shape of the cup and the mold, the upper ends of the reinforcing wires can be bent inwardly to prevent snagging of the wires during either use before or after the molding operation is completed.
One of the primary difficulties involved in a process of the general type just mentioned resides in the fact that the wire reinforcement cage has a pronounced tendency to disassemble while it is being transferred from the jig in which it is originally assembled to the mold where the rubber is cured around the cage. This tendency makes it awkward to initially assemble the swab cup prior to curing as well as being time consuming from the labor point of view, especially when assembling cups of the type wherein the wires are hooked at their lower ends and are loosely held in holes spaced around the base rings outside surface.
The prior art teaches a number of ways of holding the wires in alignment with the axis of the cup prior to and during introduction of the elastomeric blank into the cage assembly. For example, U.S. Pat. No. 2,581,981 to Taylor teaches the idea of bending the wires double and then supporting them at their lower ends by a captivating and aligning structure which grips the wires tightly while the assembled cage and a rubber blank are being molded and cured. The well swab cup disclosed by Taylor in U.S. Pat. No. 2,581,981 is partially reinforced, however, the upper region is not reinforced so that the flexibility thereof is not impaired. Taylor also discloses the use of a valve assembly to permit travel of the swabbing assembly down through the well fluid as opposed to the modern fluted mandrel.
In addition to problems which are associated with assembling the reinforcement cage, other problems have been noted during use of the swab cups in tubing and casing. In U.S. Pat. No. 2,862,776 to Bowerman the reinforcing elements of the reinforcement cage are captivated at their lower ends in the flange of a metal base in order to secure the lower ends against dislodgement, but the upper ends of the wire elements are allowed radial movement to insure the best possible sealing of the cup against the well pipe and to provide optimum swabbing action, all of which is well-known in the prior art. The Taylor and Bowerman disclosures represent innovative but now technically outdated swab cups. Most modern day swab cups are improvements and modifications to the early swab cups of Taylor and Bowerman.
Furthermore, there has been a long-felt need in the well servicing equipment industry to provide a swab cup which has an improved load carrying capability and an extended life. This need has been previously addressed by the insertion of an additional reinforcing ring into the elastomeric portion of the swab cup just inside the wire reinforcements and just above their lower ends but out of contact therewith. This ring insertion swab cup is the subject matter of U.S. Pat. No. 3,417,673 to Bowerman. The ring is shaped to prevent or limit the downward and outward flow of the elastomer of the swab cup between the reinforcing wires, as occurs when a conventional swab cup is heavily loaded and is "slumping." Such outflow of elastomer leads to pinching of the flowed materials between the swab and the wall of the pipe and to chewing off the pinched material in a manner well-known to those skilled in the art.
Various expedients have been used to try to avoid the loss of elastomer, mostly comprising the use of sleeves of harder material disposed outside and around the lower periphery of the cup. Thus, there has been a long-felt need to reduce the tendency toward mechanical failure of both the elastomer and metal parts which are incorporated into modern swab cups.
Others in the art have addressed the well-known problems, i.e. slumping, rapid wear and ability to adapt to sealing regardless of the load factor, by modifying the reinforcement cage used in the manufacture of swab cups. See for example, U.S. Pat. Nos. 3,724,337 and 3,724,338 to Richardson. The Richardson patents teach a reinforcement cage in which the cage includes inner and outer base rings which cooperate to provide a proper load support for the elastomeric body portion of the cup, while at the same time accurately aligning the lower ends of the wire members. In accordance with Richardson, wires are held tightly between a hardened outer base ring and an inner softer metal ring which has been expanded outwardly toward and against the wires to captivate their lower ends with uniform circumferential spacings while at the same time maintaining the wires in proper axial alignment to facilitate the subsequent assembly of the cage together with an elastomeric blank into a curing mold.
U.S. Pat. Nos. 3,417,673; 3,724,337 and 3,724,338 are commonly assigned. The disclosures of those three patents are hereby incorporated by reference.
The novel and unique reinforcement cage, load lifting swab cup and method for the manufacture thereof as disclosed herein have been designed to specifically address variable pressure requirements, wear characteristics and flexibility requirements of well servicing equipment. The novel, improved swab cup of this invention has been specifically designed with the maximum concentration of reinforcing wires in the area of the cup where "blow-outs" or "slumping" usually occur near the lower region. The concentration of wires molded within the rubber swab cup provides for a minimum gap between wires, the gap being filled by an elastomeric compound. When high internal pressures are encountered during the swabbing operation, the frequency of rubber failures between the wires (in the gaps) increases as the gap width between wires increase. Thus the swab cup of this invention provides for increased pressure readings, which translates into a greater amount of fluid removed from a well per swab run.
The wear resistance characteristic, which has been a constant problem with prior art swab cups, has been addressed by designing the novel swab cup of this invention with a maximum number of wires and also a longer overall length than the swab cups of the prior art. This design provides for maximum resistance to wear as the swab cups are moved up and down steel tubing in the well. This resistance to wear prevents the swab cup from prematurely losing its inherent strength due to loss of wall thickness of rubber and thickness of wires in the crucial "blow-out" area.
The novel, improved swab cup of this invention also has enhanced flexibility. The long and short wire design permits the dense concentration of wires in the lower region of the swab cup, but a lower concentration of wires at the upper end. This design feature allows the cup to be very flexible at the top, providing for a seal against the tubing with comparatively lighter loads of fluid than are usually possible with a heavy-duty wire swab cup such as the subject cup. The additional length of the longer wires, acting independently above the shorter wires facilitates loading the swab cup (sealing against the tubing) and removing lighter loads of fluid.
The combination of enhanced performance characteristics equates to a greater volume of fluid removed per run and also an increased number of runs possible per swab cup. Thus fewer swab cups are required for a given job when compared to existing technology. Furthermore, in the process of manufacturing the swab cups of this invention, as disclosed herein, the wires are molded in a prealigned condition. Such prealignment at the top of the swab cup precludes the requirement of a spacer sleeve to prevent the wires from becoming forced around a portion of the swab mandrel when running down into the tubing. This condition is common among existing swab cups in which the wires are molded straight at the top, at a diameter corresponding to the outside diameter of the cup, and then mechanically crimped inwardly.